1. Field of the Invention
The present invention relates, for example, to a color picture tube of a television receiver for household use, a color picture tube of a computer monitor and color display and a glass bulb for color picture tube used in these color picture tubes.
2. Description of the Related Art
A color picture tube is used in a variety of apparatuses for household use and industrial use such as television color picture tube, computer monitor and color display or the like. In general, a glass bulb forming a color picture tube is formed of a face plate and a funnel and the face plate and funnel are joined with a glass bonding agent. At the internal surface of face plate, light emitting material layer is provided to emit the lights of three colors of red, green and blue. Moreover, a color selection mask is provided opposed to the internal surface of the face plate within the glass bulb.
With enlargement in size of color picture tube, it is requested to use a face plate having a flat surface of a glass bulb in order to satisfy the requirement for distortion-free and more natural display. The color picture tube having such a flat face plate is already known, for example, by the Japanese Patent Application Laid-Open No. HEI 7-99030. The color picture tube disclosed in this Japanese patent application is provided with a bulb including a flat glass panel and a flat shadow mask provided opposed to the flat glass panel in this bulb.
However, in the color picture tube having a flat glass panel disclosed in the Japanese patent application laid-open No. HEI 7-99030, it is difficult to give uniform tension in both horizontal direction (X direction) and vertical direction (Y direction) of the color selection mask and a newly designed facilities which are different from the existing one to a large extend will be required. Moreover, it is also difficult to prevent vibration of color selection mask caused by the vibration applied from external side, easily resulting in a problem of deterioration of display quality due to vibration of the color selection mask. In addition, since the thickness of the flat glass panel is uniform, so-called the arch effect is not provided and strength of the glass panel for external mechanical shock is rather low and it is essential to form a thick glass panel in order to acquire the sufficient strength for explosion. When the glass panel as a whole is formed thick as explained above, not only distortion of image increased due to refraction of light at the glass panel but also weight of the color picture tube as a whole is increased. Here, the arch effect means that when the face plate of the glass bulb is projected toward outside, if a mechanical shock is applied to the frame plate from external side, a compressing force is applied to the internal surface of the face plate and thereby the shock resistance property of the face plate is increased. When an external mechanical shock is applied to the face plate of the flat glass bulb, the face plate may be broken easily because a tensile force is applied to the internal surface of the face plate.